omap: Split OMAP2_IO_ADDRESS to L3 and L4

This patch splits OMAP2_IO_ADDRESS to OMAP2_L3_IO_ADDRESS and
OMAP2_L4_IO_ADDRESS to reclaim more IO space.

The omap_read*() and omap_write*() functions will work only over
L4 address space. Current omap kernel stack uses these functions
only to access registers over L4 io address space

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>